Problem detection apparatus and method in exhaust purifying apparatus

ABSTRACT

An exhaust purifying apparatus is provided with a filter located in an exhaust path of an internal combustion engine and configured to collect particulates in exhaust gas. The exhaust purifying apparatus is also provided with a differential pressure sensor which detects the pressure difference generated between the upstream side and downstream side of the filter. The problem detection apparatus of the exhaust purifying apparatus is provided with a differential pressure calculation unit and a judgment unit. The differential pressure calculation unit calculates the pressure difference between the upstream and downstream sides of the filter based on the operating state of the internal combustion engine. The judgment unit calculates a difference P between an actual measurement value of the pressure difference and a calculation differential pressure value compares the difference P with a threshold value, and detects that the filter has a problem.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a Continuation application of PCT Application No. PCT/JP2007/074106, filed Dec. 14, 2007, which was published under PCT Article 21 (2) in Japanese.

This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2006-350134, filed Dec. 26, 2006, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a problem detection apparatus and method in an exhaust purifying apparatus, in an exhaust filtering system such as a DPF.

2. Description of the Related Art

An exhaust filtering system such as a diesel particulate filter (DPF) system has a filter inside for collecting particulates included in exhaust gas of an engine, and purifies the exhaust gas through the filter. A filter is clogged with collected particulates. Therefore, appropriate amount of the collected particulates is automatically burnt, or cleaning or replacement is urged. An increased exhaust resistance in a DPF unit may increase a backpressure and exert an influence upon control of an engine.

Therefore, a DPF unit has a differential pressure sensor for measuring a pressure difference between the upstream side and downstream side of a filter, and judges whether a filter is clogged with particulates, based on the measurement value of such a differential pressure sensor. When a filter is clogged, a DPF unit issues a signal to urge an operator to manually burn the clogged particulates, or sends such a signal to a control unit for controlling an engine.

A filter in such a DPF unit is important, and exerts a large influence upon traveling of vehicles and environment, and is subject to large temperature changes and pressure fluctuations during operation. A filter is usually made of ceramic having a number of fine perforations on the surface, and may cause a leak of exhaust gas through a crack caused by an overload or a molten defect.

If particulates are deposited on a filter, the measurement value of a differential pressure sensor is increased by the deposited particulates. However, if a filter has a crack or a molten defect, the differential pressure increase caused by the deposited particulates is cancelled, and the differential pressure sensor can indicate a normal value in spite of deposition of particulates.

For, example, Jpn. Pat. Appln. KOKAI Publication No. 2003-155920 discloses the invention of a problem detection apparatus for a particulate filter. In the disclosed apparatus, a pressure difference before and after a particulate filter is measured by a differential pressure sensor, the measured differential pressure value is compensated by deposition of ash, and a particulate filter is checked for a clogging and a molten defect.

BRIEF SUMMARY OF THE INVENTION

There are following problems in a conventional problem detection apparatus for a particulate filter.

In a problem detection apparatus for a particulate filter, a diagnosis is started only when an engine is judged steady. A threshold value used for the judgment is determined by an average engine speed and a time required to inject fuel, and is not determined unless the steady state of an engine is continued for a predetermined time. Thus, a diagnosis is not executed.

Further, a threshold value used for the judgment is determined irrespective of deposition of particulates. Therefore, a threshold value needs to be determined in expectation of an increase in backpressure by deposition of particulates. However, an ash calculation deposition value used for correcting a differential pressure is calculated simply proportional to a vehicle traveling distance. Therefore, even if the ash deposition amount becomes different depending on a driving history, the difference in the ash deposition amount is not reflected on the decision of a threshold value used for the judgment.

The present invention has been made in order to solve the above problems, and to provide a problem detection apparatus in an exhaust filtering system, which is configured to exactly detect a problem in a filter.

The problem detection apparatus in an exhaust filtering system of the present invention is configured as follow.

1. A problem detection apparatus in an exhaust purifying apparatus having a filter which is provided in an exhaust path in an internal combustion engine, and collects particulates in exhaust gas, and a differential pressure sensor which detects a pressure difference generated between the upstream side and downstream side of the filter, the problem detection apparatus comprising a differential pressure calculation means which calculates a value of a pressure difference between the upstream and downstream sides of the filter based on an operating state of the internal combustion engine; and a judgment means which calculates a difference P between an actual measurement value of the pressure difference between the upstream side and downstream side of the filter detected by the differential pressure sensor and a calculation differential pressure value from the differential pressure value calculation means, compares the difference P with a threshold value, and detects that the filter has a problem.

2. The problem detection apparatus in the exhaust purifying apparatus according to claim 1, wherein the judgment means has a first threshold value used for judging a clogging of the filter, and a second threshold value used for judging a leak of the filter, and judges that the filter has a problem, when a value of the difference P exceeds the first threshold value, or when a value of the difference P exceeds the second threshold value.

3. The problem detection apparatus in the exhaust purifying apparatus according to claim 2, wherein the first threshold value is calculated from an exhaust flow rate, and a clogging coefficient based on a soot calculation deposition value and ash calculation deposition value of the filter; and the second threshold value is calculated from an exhaust flow rate, and a leak coefficient based on a soot calculation deposition value and ash calculation deposition value of the filter.

4. The problem detection apparatus in the exhaust purifying apparatus according to claim 3, wherein the differential pressure calculation means calculates a calculation differential pressure value based on a reference differential pressure value calculated from temperature and exhaust flow rate in the upstream side of the filter.

5. The problem detection apparatus in the exhaust purifying apparatus according to any one of claims 1 to 4, wherein the judgment means has a decision means which decides that the filter has a problem when the filter is judged defective and the judgment is continued for a predetermined time.

6. A problem detection method in an exhaust purifying apparatus having a filter which is provided in an exhaust path in an internal combustion engine, and collects particulates in exhaust gas, wherein a differential pressure sensor for detecting a pressure difference between the upstream side and downstream side of the filter detects a pressure difference between the upstream side and downstream side of the filter; a differential pressure calculation means for calculating a value of a pressure difference between the upstream side and downstream side of the filter based on an operating state of the internal combustion engine calculates a pressure difference between the upstream side and downstream side of the filter; and a judgment means calculates a difference P between an actual measurement value of the pressure difference between the upstream side and downstream side of the filter detected by the differential pressure sensor and a calculation differential pressure value calculated by the differential pressure value calculation means, compares the difference P with a threshold value, and judges whether the filter has a problem.

7. The problem detection method in the exhaust purifying apparatus according to claim 6, wherein the judgment means judges that the filter has a problem, when a value of the difference P exceeds the first threshold value, or when a value of the difference P exceeds the second threshold value.

8. The problem detection method in the exhaust purifying apparatus according to claim 7, wherein the first threshold is a value calculated from an exhaust flow rate, and a clogging coefficient based on a soot calculation deposition value and ash calculation deposition value of the filter; and the second threshold value is a value calculated from an exhaust flow rate, and a leak coefficient based on a soot calculation deposition value and ash calculation deposition value of the filter.

9. The problem detection method in the exhaust purifying apparatus according to claim 8, wherein the calculation differential pressure value calculated by the differential pressure calculation means is a value calculated based on a reference differential pressure value calculated from temperature and exhaust flow rate in the upstream side of the filter.

10. The problem detection method in the exhaust purifying apparatus according to any one of claims 6 to 9, wherein the judgment means judges that the filter has a problem, when the filter is judged defective and the judgment is continued for a predetermined time.

EFFECTS OF THE INVENTION

A problem detection apparatus and method in an exhaust filtering system according to the present invention has the following effects.

A filter problem can be detected by calculating a calculation differential pressure value even in an unsteady traveling state. As a threshold value is sequentially calculated from a traveling state, a filter problem can be detected by comparing with a threshold value even in an unsteady traveling state.

A soot deposition value is calculated by considering a loss caused by Nox and heat, and a threshold value is corrected based on such a soot deposition value. Therefore, the calculated value reflects an actual driving history, and a problem can be detected by using an appropriate threshold value.

An ash deposition value is calculated by using a total fuel injection amount, and the calculated value reflects an actual driving history more than in a case of calculation based on a traveling distance.

A clogging of a filter and a leak caused by a crack can be detected. As a filter problem is checked after a lapse of certain time, the reliability of the problem detection apparatus can be increased.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a diagram showing the configuration of an engine having an embodiment of a problem detection apparatus according to the present invention;

FIG. 2 is a block diagram of a problem detection apparatus;

FIG. 3 is a block diagram of a control unit;

FIG. 4 is a block diagram of a soot deposition value calculation means;

FIG. 5 is a block diagram of a threshold value calculation means;

FIG. 6 is a block diagram of a judgment means;

FIG. 7 is a diagram showing a map for obtaining a reference soot generation value;

FIG. 8 is a graph showing a coefficient of fuel injection amount;

FIG. 9 is a graph showing a coefficient of a cooling water temperature;

FIG. 10 is a graph showing a coefficient of a cooling water temperature;

FIG. 11 is a graph showing a coefficient of a soot deposition value; and

FIG. 12 is a flowchart of operation.

DETAILED DESCRIPTION OF THE INVENTION

Explanations will be given on an embodiment of a filter problem detection apparatus and method according to the present invention with reference to the accompanying drawings.

FIG. 1 shows the configuration of an engine 12 having a filter problem detection apparatus 10, as an internal combustion engine. The engine 12 is a diesel engine comprising a turbo charger 14, a DPF unit 16, a fuel supply unit 18, and an engine speed sensor 19. The turbo charger 14 is connected to an exhaust pipe 20 as an exhaust path, and a suction pipe 22 as a suction path. The turbo charger 14 pressurizes outside air suctioned through an air cleaner 24 by using an exhaust pressure, and feeds the pressurized air to the engine 12.

The suction pipe 22 is provided with a suction pressure sensor 26 to detect the pressure in the suction pipe 22, or the boost pressure by the turbo charger 14, and a suction flow rate sensor 27 to detect a flow rate in the suction pipe 22. The engine 12 is not limited to a diesel engine, but may be a natural suction engine not provided with the turbo charger 14.

The DPF unit 16 is cylindrical, and includes a filter 28 inside. In the DPF unit 16, the upstream side is connected to the exhaust side of the turbo charger 14, and the downstream side is connected to the exhaust port 29 of a vehicle. The filter 28 is a ceramic filter, and has a surface having fine perforation to collect particulates included in exhaust gas. The DPF unit 16 is provided with an upstream side pressure sensor 30, a differential pressure sensor 32, an upstream side temperature sensor 35, and a downstream side temperature sensor 37. The DPF unit 16 is provided with catalysts 31 and 33 in the front and rear parts, respectively.

The upstream side pressure sensor 30 is provided in the upstream side of the filter 28, and detects a pressure value in the upstream side of the filter 28. The difference pressure sensor 32 is detects a pressure difference generated between the upstream side and downstream side of the filter 28. The upstream side temperature sensor 35 measures a temperature in the upstream side of the filter 28, or a temperature of exhaust gas flowing into the filter 28. The downstream side temperature sensor 37 measures a temperature in the downstream side of the filter 28.

Each sensor is connected to the control unit 36 (electronic control unit [ECU]), as shown in FIG. 2. The control unit 26 is also connected to various sensors, such as an atmospheric pressure sensor 38 to detect the value of atmospheric pressure, and a water temperature sensor 40 to detect a temperature of a cooling water, as shown in FIG. 2. The values detected by these sensors are sent to the control unit 36.

The fuel supply unit 18 is a fuel injection unit to inject fuel. The fuel supply unit 18 injects predetermined amount of fuel into the engine 12 according the instruction from the control unit 36.

As shown in FIG. 3, the control unit 36 has a judgment unit 44, a soot deposition value calculation means 46, an ash deposition value calculation means 47, a threshold value calculation means 48, a differential pressure calculation means 50, a clocking means 60, and a decision means 62.

As shown in FIG. 4, the soot deposition value calculation means 46 comprises a soot generation amount calculation means 52, a Nox amount calculation means 54, a soot loss amount (Nox) calculation means 56, a soot loss amount (heat) calculation means 58, and a totalizing means 59.

The soot generation amount calculation means 52 calculates a reference soot generation value from the engine speed detected by the engine speed sensor 19 and the amount of fuel supplied from the fuel supply unit 18 to the engine 12, by using a map 1 shown in FIG. 7. Further, the soot generation amount calculation means 52 calculates a soot calculation emission value by correcting the reference soot generation value by using correction graphs shown in FIG. 8 and FIG. 9.

The map 1 is a three-dimensional map expressing a reference soot generation amount (value) in the direction vertical to the paper surface, in which a horizontal axis along the paper surface represents an engine speed Ne, and a vertical axis represents a fuel supply (injection) amount q. FIG. 8 is a graph showing a value for correcting the reference soot generation amount (value) for the fuel injection amount. FIG. 9 is a graph showing a value for correcting the reference soot generation amount (value) for the cooling water temperature.

The Nox amount calculation means 54 calculates the Nox emission amount, or a reference generation amount, from the engine speed detected by the engine speed sensor 19 and the amount of fuel supplied from the fuel supply unit 18 to the engine 12, by using a map 2 (not shown). The map 2 is a three-dimensional map, as is the map 1. The Nox amount calculation means 54 calculates the Nox calculation generation value by correcting the reference Nox generation amount by using a correction graph of FIG. 10. FIG. 10 is a correction graph showing a coefficient for the cooling water temperature.

The soot loss amount (Nox) calculation means 56 calculates a soot calculation loss value (Nox) from a ratio A between the soot calculation generation value calculated by the soot generation amount calculation means 52 and the Nox calculation generation value calculated by the Nox amount calculation means 54, and the upstream side temperature of the filter 28 measured by the upstream side temperature sensor 35, by using a map 3 (not shown). The map 3 is a three-dimensional map, as is the map 1.

The soot loss amount (heat) calculation means 58 detects an air-to-fuel ratio (an excessive air rate) from the flow rate in the suction pipe 22 detected by the suction flow rate sensor 27 and the amount of fuel supplied from the fuel supply unit 18 to the engine 12. The soot loss amount (heat) calculation means 58 calculates a reference soot loss value (heat) from the air-to-fuel ratio, and the upstream side temperature of the filter detected by the upstream side temperature sensor 35, by using a map 4. The map 4 is a three-dimensional map, as is the map 1. Further, the soot loss amount (heat) calculation means 58 calculates a soot calculation loss value (heat) by multiplying the reference soot loss value (heat) by the coefficient obtained by using the correction graph show in FIG. 11. The soot deposition value expressed on the horizontal axis of the correction graph shown in FIG. 11 indicates a soot deposition value up to the present time.

The soot calculation emission value, soot calculation loss value (Nox) and soot calculation loss value (heat) are calculated as above. After these values are calculated, the soot calculation loss value (Nox) and soot calculation loss value (heat) are subtracted from the soot calculation emission value, and the soot calculation generation value is calculated. The totaling means 59 totalizes the soot calculation generation value, and calculates a soot deposition value up to the present time, that is, a soot calculation deposition value.

The ash deposition value calculation means 47 calculates an ash generation value by multiplying the amount of fuel supplied from the fuel supply unit 18 to the engine 12 by a coefficient. The ash deposition value calculation means 47 calculates an ash calculation deposition value by totalizing the ash calculation generation value (amount).

The threshold value calculation means 48 comprises a first threshold value calculation means 64 and a second threshold value calculation means 66, as shown in FIG. 5.

The first threshold value calculation means 64 calculates a coefficient (clogging) from the soot calculation deposition value and ash calculation deposition value, by using a map 5 (not shown). The map 5 is a three-dimensional map, as is the map 1. Next, the first threshold value calculation means 64 calculates a first threshold value from a coefficient (clogging) and exhaust flow rate, by using a map 6 (not shown). The map 6 is a three-dimensional map, as is the map 1. The exhaust flow rate is calculated from the flow rate in the suction pipe 22 detected by the suction flow rate sensor 27, the fuel supply amount to the engine 12, the upstream side pressure of the filter 28 detected by the upstream side pressure sensor 30, and a gas constant.

The second threshold calculation means 66 calculates a coefficient (leak) from the soot calculation deposition value and ash calculation deposition value, by using a map 7 (not shown). The map 7 is a three-dimensional map, as is the map 1. Then, the second threshold calculation means 66 calculates a second threshold value from a coefficient (leak) and exhaust flow rate, by using a map 8 (not shown). The map 8 is a three-dimensional map, as is the map 1.

The differential pressure calculation means 50 calculates a calculation differential pressure value (clogging) and a calculation differential pressure value (leak) by multiplying the reference differential pressure value obtained from the exhaust flow rate and the upstream side temperature of the filter 28, by the coefficients of map 5 and map 7.

A judgment means 44 comprises a clogging judgment means 68 and a leak generation judgment means 70, as shown in FIG. 6.

The clogging judgment means 68 calculates a difference P1 by subtracting the calculation differential pressure value (clogging) calculated by the differential pressure value calculation means 50 from the measurement differential pressure value detected by the differential pressure sensor 32. Further, the clogging judgment means 68 compares the difference P1 with the first threshold value calculated by the first threshold value calculation means 64, and judges clogging when the difference P1 is larger than the first threshold value.

The leak generation judgment means 70 calculates a difference P2 by subtracting the measurement differential pressure value detected by the differential pressure sensor 32 from the calculation differential pressure value (leak) calculated by the differential pressure value calculation means 50. Further, the leak generation judgment means 70 compares the difference P2 with the second threshold value calculated by the second threshold value calculation means 66, and judges a leak when the difference P2 is larger than the second threshold value.

The clocking means 60 measures the duration time of the judgment by the judgment means 44. The decision means 62 decides a problem, when the time measured by the clocking means 60 exceeds a previously input decision time. The decision time is 10 seconds, for example. The decision time may be changed if necessary.

Next, an explanation will be given on the flow of a problem detection method using the filter problem detection apparatus 10 with reference to the flowchart of FIG. 12.

First, a sampling time a and a deciding time T are determined (S1). The sampling time a is a time interval in repeating comparison of the threshold value and pressure difference. The deciding time T is a time (decision time) required to decide a problem. Then, the time t is set to zero as an initial value (S2).

Next, the control unit 36 receives the detected values sent from the water temperature sensor 40, atmospheric pressure sensor 38, engine speed sensor 19, and suction temperature sensor (not shown) (S3). The control unit 36 judges whether it is possible to detect a problem of the filter 28 built in the DPF unit 16 from the received detected values. Namely, the control unit 36 confirms that the engine is not started immediately before, the operation is not abnormal, or any one of the sensors is not defective.

When the additional condition is set up and detection of a problem of the filter 28 is judged possible in step S4, step S5 is taken place. In step S5, the soot calculation generation amount is calculated as described above based on the value sent from each sensor. Then, in step S6, the calculated generation value is sequentially totalized, and the soot calculation deposition value is calculated. Similarly, the ash calculation generation value is calculated as described above (S7), and the calculated generation value is sequentially totalized, and the ash calculation deposition value is calculated (S8).

Further, the first and second threshold values and the calculation differential pressure value are calculated as described above from the value sent from each sensor (S9, S19, S11). After the calculation differential pressure value (clogging and leak) and the first and second threshold values are calculated as described above, the difference P1 between the calculation differential pressure value (clogging) and the measurement value of the differential pressure sensor 32, and the difference P2 between the calculation differential pressure value (leak) and the measurement value of the differential pressure sensor 32, are calculated (S12). Then, the difference P1 is compared with the first threshold value (S13). When NO is judged, step S14 is taken place. When YES is judged, step S15 is taken place.

In step S14, the difference P2 is compared with the second threshold value. When NO is judged, step S2 is taken place. When YES is judged, step S15 is taken place. In step S15, the sampling time a is added to the time t, and the sum is taken as a new time t. Then, whether the time t exceeds the decision time T is judged (S16). When NO is judged, the operation step goes back to step S3. In step S3, the operation steps are repeated from step S3. When YES is judged for the difference from the threshold value, step S15 is taken place. The sampling time a is added to the time t, and the operation is repeated until the time t exceeds the decision time T.

If NO is judged for the difference from the threshold value in step S13 or S14 during repetition of steps, step S2 is taken place. The operation is restarted by setting the time t to zero.

When the time t exceeds the decision time T in S16, step S17 is taken place, and the decision means 62 judges that a clogging or leak occurs in the filter 28, and the filter is defective.

As explained above, the problem detection apparatus 10 judges a problem such as a clogging and leak in the filter 28 by comparing with a threshold value. Further, a threshold value is a value obtainable any time during traveling of vehicles, and a problem in the filter 28 can be securely judged even if the engine 12 is not driven in a steady state.

The present invention can be used as a problem detection apparatus and method in an exhaust filtering apparatus. 

1. A problem detection apparatus in an exhaust purifying apparatus having a filter which is provided in an exhaust path in an internal combustion engine, and collects particulates in exhaust gas, and a differential pressure sensor which detects a pressure difference generated between the upstream side and downstream side of the filter, the problem detection apparatus comprising: a differential pressure calculation means which calculates a value of a pressure difference between the upstream and downstream sides of the filter based on an operating state of the internal combustion engine; and a judgment means which calculates a difference P between an actual measurement value of the pressure difference between the upstream side and downstream side of the filter detected by the differential pressure sensor and the calculation differential pressure value from the differential pressure value calculation means, compares the difference P with a threshold value, and detects that the filter has a problem.
 2. The problem detection apparatus in the exhaust purifying apparatus according to claim 1, wherein the judgment means has a first threshold value used for judging a clogging of the filter, and a second threshold value used for judgment a leak of the filter, and judges that the filter has a problem, when a value of the difference P exceeds the first threshold value, or when a value of the difference P exceeds the second threshold value.
 3. The problem detection apparatus in the exhaust purifying apparatus according to claim 2, wherein the first threshold value is calculated from an exhaust flow rate, and a clogging coefficient based on a soot calculation deposition value and ash calculation deposition value of the filter; and the second threshold value is calculated from an exhaust flow rate, and a leak coefficient based on a soot calculation deposition value and ash calculation deposition value of the filter.
 4. The problem detection apparatus in the exhaust purifying apparatus according to claim 3, wherein the differential pressure calculation means calculates a calculation differential pressure value based on a reference differential pressure value calculated from temperature and exhaust flow rate in the upstream side of the filter.
 5. The problem detection apparatus in the exhaust purifying apparatus according to any one of claims 1 to 4, wherein the judgment means has a decision means which decided that the filter is defective when the filter is judged defective and the judgment is continued for a predetermined time.
 6. A problem detection method in an exhaust purifying apparatus having a filter which is provided in an exhaust path in an internal combustion engine, and collects particulates in exhaust gas, wherein a differential pressure sensor for detecting a pressure difference between the upstream side and downstream side of the filter detects a pressure difference between the upstream side and downstream side of the filter; a differential pressure calculation means for calculating a value of a pressure difference between the upstream side and downstream side of the filter based on an operating state of the internal combustion engine calculates a pressure difference between the upstream side and downstream side of the filter; and a judgment means calculates a difference P between an actual measurement value of a pressure difference between the upstream side and downstream side of the filter detected by the differential pressure sensor and a calculation differential pressure value calculated by the differential pressure value calculation means, compares the difference P with a threshold value, and judges whether the filter has a problem.
 7. The problem detection method in the exhaust purifying apparatus according to claim 6, wherein the judgment means judges that the filter has a problem, when a value of the difference P exceeds the first threshold value, or when a value of the difference P exceeds the second threshold value.
 8. The problem detection method in the exhaust purifying apparatus according to claim 7, wherein the first threshold is a value calculated from an exhaust flow rate, and a clogging coefficient based on a soot calculation deposition value and ash calculation deposition value of the filter; and the second threshold value is a value calculated from an exhaust flow rate, and a leak coefficient based on a soot calculation deposition value and ash calculation deposition value of the filter.
 9. The problem detection method in the exhaust purifying apparatus according to claim 8, wherein the calculation differential pressure value calculated by the differential pressure calculation means is a value calculated based on a reference differential pressure value calculated from temperature and exhaust flow rate in the upstream side of the filter.
 10. The problem detection method in the exhaust purifying apparatus according to any one of claims 6 to 9, wherein the judgment means judges that the filter has a problem, when the filter is judged defective and the judgment is continued for a predetermined time. 